Precoated Layers - Why

In the first edition of Stahl s laboratory handbook Durmschicht-Chromatographie published in 1962, equipment for coating glass plates is illustrated, and detailed procedures for the preparation of TLC plates are described. Even today, TLC sorbents for a manual coating operation are produced in an only shghtly modified form, especially where labor costs are small and time is a minor consideration. The layers obtained often show good selectivity, but do not achieve the separation efficiency obtained by precoated layers and seldom lead to reproducible results. 

If TLC is used as an analytical method in quality control, the reproducibUity, i.e. lack of scatter (precision of both system and method), and also the accuracy of the analytical results must be determined. The GMP/GLP guidelines also require vahdation of the method, i.e. testing for linearity, selectivity, robustness and limits of detection and determination (see also Section 9.1 Validation of TLC Methods ). For method development, high demands are placed on the stationary phases of the chromatographic system  

When precoated layers supphed by a manufacturer are accompanied by a DIN/ISO 9001 certificate, it can be assumed that constant quahty of hardware for the TLC is being maintained. By standardizing the most important operations in the TLC over several years, very reproducible results are obtained [10]. 

in-house production of layers for TLC is not therefore a sensible option in industrial, pharmaceutical or official laboratories. To save time and to obtain good results, commercially available precoated layers must be used. 

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